Rotary pulp screens



Aug. 11, 1959 B. cowAN ETAL ROTARY PULP SCREENS 2 Sheets-Sheet 1 FiledOct. 24, 1955 INVENTORS fl C 0 wan 5 I C 0 ma n Aug. 11, 1959 B. cowANET AL 2,899,064

ROTARY PULP SCREENS Filed Oct. 24, 1955 2 Sheets-Sheet 2 q 7 Sm-M F115 521 INVENTORS 6 fiowan 5. Cowan United States Patent fitice 2,899,064Patented Aug. 11, 1959 ROTARY PULP SCREENS Ben Cowan and Elijah Cowan,Montreal, Quebec, Canada Application October 24, 1955, Serial No.542,360

Claims. (Cl. 210-219) This invention relates to rotary pulp screens andmore particularly to the horizontal type in which the rotating elementor impeller is sectionalized for progressive dilution by the incomingstock and of the thickening mass of pulp which tends to build up on thescreen, and by so do ing eliminate entirely or almost entirely thenecessity for introducing a further supply of fresh or white water tocomplete the screening and carry off the tailings at the dischargeoutlet.

The invention consists essentially in the provision of a rotary impellerwhich is sectionalized by bafiies disposed at right angles to the axisof rotation of the impeller, the baffles being provided with apertureswhich allow a portion of the incoming stock to pass through from onesection to another to assist in diluting the thickening fibres in thescreen which accumulate towards the discharge end of the screen.

The incoming pulp stock is prepared having a desired consistency, andwith the screens heretofore used, only the first portion of the screenfunctioned efiiciently with the fibres matting on the screen in everincreasing thickness towards the discharge opening. In orderto-ove'rcome this matting of the pulp, fresh or white water has had tobe introduced in an attempt to break up-the matting pulp. This may ormay not be satisfactory depending on working conditions, but in anycase, contributed-tonncontrolled dilution of the pulp stock withresulting decrease in efiiciency. This difficulty has-beenovercorne inthe present invention where a portion of the initial pulp stock isby-passed directly to a second or more stages thereby giving a more evendistribution of the pulp stock, in its original state of dilution, overa greater length of screen so that the pulp screening willbeevenlydistributed over a greater length of the machine and will not tend tobuild up a pulp mat as has been the case heretofore. Any diluent whichmay have to be added is merely to ensure that the tailings will becleared from the end portion of the rotary screen and carried outthrough the discharge opening.

The primary object of the invention therefore is to maintain theconsistency of the incoming pulp stock over the full length of therotary screen and thereby eliminate to a large extent uneven matting onthe screen surface.

A further object of the invention is to sectionalize the impeller of arotary pulp screen and to bypass a portion of the incoming pulp stock toeach section without further dilution.

A further object of the invention is to provide a rotary to assist inthe removal of the rejects or tailings without in any way diluting themain stock flow.

These and other objects will be apparent from the drawings in which Fig.1 is a vertical section elevation of a rotary screen having a primaryand one secondary screening zone.

Fig. 2 is a cross section of the impeller taken on the line 2-2 of Fig.1.

Fig. 3 is a cross section of the impeller taken on the line 33 of Fig. land showing the pulp stock by-pass openings in the baffle.

Fig. 4 is a cross section of the impeller taken on the line 4-4 of Fig.l and showing the supplementary dilution apertures, if required.

Fig. 5 is a vertical section elevation of a rotary screen withadditional secondary screening zones and limited dilution waterapertures, if required.

Fig. 6 is a diagrammatic sketch showing the main stock flow in therotary screen shown in Fig. 1.

Fig. 7 is a diagrammatic sketch showing the main stock flow in therotary screen shown in Fig. 5.

Referring to the drawings and particularly to Figs. 1, .2, '3, -4 and 6.The rotary pulp screen is of the horizontal type and comprises acircular casing I mounted on the base 2 and closed around its peripheryby the cover 3. The casing 1 is provided with a large diameter pulpstock inlet 4 and a rejects or tailings outlet '5. The drive shaft 6comprises a sleeve shaft 7 and a stub shaft 8 sealing the inner end ofthe sleeve shaft. The sleeve shaft 7 is *jounnalled in the bearing 9 onthe side of the casing 1 while the stub shaft 8 is journalled in anextension bearing 10 built onto the wall of the stock inlet 4.

The impeller of the rotary screen is built up on the sleeve hub 11secured to the drive sleeve 7 for rotation therewith. The impeller iscomposed .of a series of blades 12 set at a slight angle longitudinallyof the hub sleeve -11 and radiating therefrom and are held rigidly bymeans of the end rings 13 and 14 and by the intermediately disposedbaflie plates 15 and 16.

A sleeve 17 extends between the end ring 13 and the bafiie plate 15 andhas an internal diameter equal to and concentric with the stock inlet 4at its point of entry to the casing 1. This sleeve 17 is provided with aseries of longitudinal slots 18 through which the stock flows from theinlet 4 into what may be called the primary screening zone A of thescreen.

The baffle plate 15 is provided with a series of apertures 19 set at aradius within the diameter of the sleeve 17 and serves to by-passdirectly, .a flow of pulp stock from the inlet 4 through the sleeve 17to the space between the baflles 15 and 16 which may be called thesecondary screening zone B.

The sleeve shaft 7 and the hub sleeve 11 in the length between thebaffle plate 16 and the discharge end of the rotary screen, is providedwith a series of apertures 20 connecting the bore of the shaft sleeve 7with the interior of the rotary screen to provide a series of waterjets. The number and spacing of these apertures 20 will depend on thevolume of diluent water required to break up any fibrous matting tendingto form on the screen 21 towards the discharge end and to assist incarrying off the rejects or tailings out through the discharge opening5. The stub shaft 8 is fitted longitudinally in the sleeve shaft 7 sothat its end 22 provides a plug to the sleeve 7 at a point adjacent theinner circle of apertures 20.

In. Fig. 5 of the drawings a modified form of the rotary screen isshown. In this form an additional bafiie 30 is shown which, acting inconjunction with the baffle 16, provides an additional secondaryscreening zone C. In this modification the baffle 16 is provided with aseries of apertures 31, and the battle 30 has similar apertures 32. Theapertures 19, 31 and 32 are preferably set in this case the bore of thesleeve 7 with the screening zone D. The purpose of these apertures 33 ismerely to ensure that the rejects or tailings are carried out throughthe discharge opening 5. However, these apertures 33 can be dispensedwith, as shown in Fig. 7, if the flow of primary pulp stock from theinlet 4 and carried through the sleeve 17 and apertures 19, 31 and 32 ismade adequate to carry out the final screening in the zone D and carryaway the rejects or tailings through the discharge opening 5.

In the operation of this invention, reference is made to Figs. 6 and 7of the drawings, Fig. 6 is a diagrammatic representation of the rotaryscreen shown in Fig. 1 while Fig. 7 is a diagrammatic representation ofthe screen shown in Fig. 5.

In Fig. 6 the flow of pulp stock is shown by the arrows 40 as passingfrom the inlet 4 into the sleeve 17 where a large portion of the stockis passed into the primary screening zone A, Where little or no mattingof the pulp takes place on the screen 21. As the pulp matting tends tobuild up towards the discharge end of the screen, this tendency will begreatly reduced by the flow of the stock from the sleeve 17 through theapertures 19 into the secondary screening zone B. The flow of stockdirectly onto the screen 21 in the area of the zone B will ensure amaximum passage through the screen of screenable stock and furtherreducing the matting tendency in this area. The diluent required to bepassed into the rotary screen through the apertures 20 will be reducedto a minimum and will only be sufficient to reduce matting to a minimumand carry off the tailings to the discharge outlet 5.

In Fig. 7 it will be seen that the stock is directed into all screeningzones A, B, C and D so that the pulp fibres are screened evenly over thewhole length of the screen 21. diluent needs to be added to the zone D,and if it is added it is only for the purpose of speeding up thedischarge of the tailings through the discharge opening 5.

The rotary pulp screen as described above ensures that a maximum ofscreening will be effected over a longer period of time without havingto stop for cleaning purposes. In addition the screening can be carriedout using only a minimum of diluent or none at all depending on thenumber of secondary screening zones used in the With such a spread ofthe pulp stock little or no I sectionalized along its length by baiflesset transversely 7 of the axis of the impeller, an axial sleeve in thefirst section of the impeller, said sleeve being approximately the samediameter as the said axial pulp supply inlet, said sleeve having aseries of longitudinal slots allowing a large portion of the pulp stocksupply to be directed onto 7 said screen, the said bafiles having aseries of apertures through which the remainder of the pulp stock fromsaid sleeve passes into the various sections of the impeller to spreadthe pulp stock over a greater area of the screen.

2, In a rotary pulp screening machine including a' screen and a rotaryimpeller, a pulp supply inlet located axially with respect to saidimpeller, said impeller having .4 a series of blades set longitudinallyfor the length of said impeller and radiating from the axis thereof andsectionalized along its length by baffles set transversely of the axisof the impeller, an axial sleeve in the first section of the impeller,said sleeve being approximately the same diameter as the said axial pulpsupply inlet, said sleeve having a series of longitudinal slots allowinga large portion of the pulp stock supply to be directed on to saidscreen, the said baffies having a series of apertures through which theremainder of the pulp stock from said sleeve passes into the varioussections of the impeller to spread the pulp stock over a greater area ofthe screen.

3. In a rotary pulp screening machine including a screen and a rotaryimpeller, a pulp supply inlet located axially with respect to saidimpeller, said impeller having a series of blades set longitudinally forthe length of said impeller and radiating from the axis thereof andsectionalized along its length by baflles set transversely of the axisof the impeller, an axial sleeve joining the walls of the bafilesforming the first section of the impeller, said sleeve beingapproximately the same diameter as the said axial pulp supply inlet andin communication therewith, said sleeve having a series of longitudinalslots located between the blades of the impeller and allowing a largeportion of the pulp stock supply to be directed onto said screen, saidbafiies being provided with a series of apertures through which theremainder of the pulp stock from said sleeve to pass through saidbafl'les into the various sections of the impeller to spread the pulpstock over a greater part of the screen.

4. In a rotary pulp screening machine as set forth in claim 3, whereinthe apertures in the various bafiies are set at a slight anglelongitudinally with respect to the axis of the impeller and opening outtowards the discharge end of the screening machine.

5. In a rotary pulp screening machine including a screen and a rotaryimpeller, a drive shaft for said impeller said drive shaft beingpartially hollow into which is fed a supply of diluting water, a pulpsupply inlet located axially with respect to said impeller, saidimpeller having a series of blades set longitudinally for the length ofsaid impeller and radiating from the axis thereof and sectionalizedalong its length by bafiles set transversely of the axis of theimpeller, an axial sleeve joining the walls of the baffles forming thefirst section of the impeller, said sleeve being approximately the sameinternal diameter as the said axial pulp supply inlet, said sleevehaving a series of longitudinal slots allowing a large portion of thepulp stock supply to be directed onto said screen, means to pass theremainder of the pulp stock from said sleeve through said baflies intothe various sections of the impeller, to spread the pulp stock over agreater area of the screen, said drive shaft having a series 'ofapertures in its hollow section allowing a fiow of diluent water intothe last section of the impeller.

References Cited in the file of this patent UNITED STATES PATENTS

